In recent years, thermoplastic elastomers which are a rubber-like soft material not requiring a vulcanization process while having a mold processability similar to a thermoplastic resin have been used in the fields such as automobile parts, consumer electric appliance parts, electric wire coverings, medical care parts, footwear shoes, and sundry goods. Among the thermoplastic elastomers, styrene-based thermoplastic elastomers typically represented by a block copolymer or a hydrogenated product thereof are used as materials having excellent flexibility, mold processability, and so forth wherein the block copolymer or the hydrogenated product thereof has a polymer block including a structural unit derived from an aromatic vinyl compound and a polymer block including a structural unit derived from a conjugated diene compound; however, they are required to have improved abrasion resistance.
Meanwhile, the present applicant previously developed a following composition (1) as a thermoplastic elastomer which is excellent in recovery from distortion at a high temperature (heat resistance), mold processability, rubber characteristics, and flexibility (see PTL 1).
(1) A thermoplastic elastomer composition, wherein the composition is obtained by dynamically crosslinking a mixture under a molten condition thereof, the mixture having the mixing ratio: 100 parts by mass of at least one addition-polymerized block copolymer (I0) selected from the group consisting of a block copolymer and a hydrogenated product thereof, wherein the block copolymer and the hydrogenated product thereof contain one or more polymer block (A) including a structural unit derived from an aromatic vinyl compound and one or more polymer block (B) including a structural unit derived from a conjugated diene compound, and the polymer block (A) contains 1% by mass of a structural unit derived from an alkylstyrene in which at least one alkyl group having 1 to 8 carbon atoms is bonded to a benzene ring thereof; 10 parts by mass to 300 parts by mass of a polyolefin (II); 0 part by mass to 300 parts by mass of a softener for rubber (III); and 0.1 parts by mass to 20 parts by mass of a crosslinking agent (IV); and further the addition-polymerized block copolymer (I0) is crosslinked at least in a portion of the polymer block (A) in the thermoplastic elastomer composition.
And thereafter, the present applicant further developed the following composition (2) as a thermoplastic elastomer composition giving a molded article which is excellent in recovery from distortion at a high temperature (heat resistance), extrusion-mold processability, and surface properties (see PTL 2).
(2) A thermoplastic elastomer composition, wherein the composition is obtained by heat treating a mixture under a molten condition thereof, the mixture including: 100 parts by mass of at least one addition-polymerized block copolymer (I) selected from the group consisting of a block copolymer and a hydrogenated product thereof, wherein the block copolymer and the hydrogenated product thereof contain a polymer block A mainly including a structural unit derived from an aromatic vinyl compound and contains 1% by mass or more of a structural unit (a) derived from an alkylstyrene in which an alkyl group having 1 to 8 carbon atoms is bonded to a benzene ring thereof and a polymer block B mainly including a structural unit derived from a conjugated diene compound; 10 parts by mass to 300 parts by mass of an olefin-based resin (II); 0.01 parts by mass to 20 parts by mass of a crosslinking agent (III); 0.5 parts by mass to 50 parts by mass of a crosslinking adjuvant (IV) having 2 or more methacryloyl group and hydroxyl group; and 30 parts by mass to 250 parts by mass of a softener for rubber (V); and the crosslinking agent (III) is an organic peroxide.